Interpretive Summary: Parasitic ants are ant species that have evolved mechanisms to integrate in their host ant species. The process involves some form of host queen usurpation by the parasitic ant queen(s). This generally leads to the premature death of the parasitized colony. Understanding this process is interesting evolutionarily and for reasons related to the potential use of parasitic ants in the biocontrol of pest ant species. Scientists at the Center for Medical, Agricultural, and Veterinary Entomology, USDA, ARS, Gainesville, Florida, The City University of New York, and Clarkson University, Potsdam, New York, determined that newly mated queens of the slave-maker parasitic ant species, Polyergus breviceps, are able to differentiate immature host Formica colonies from mature colonies. This ability increases the survival rate of the parasitic species, since they require fully mature host colonies to provide their slave work force. The cues are likely to be chemical in nature. While the transfer of cuticular hydrocarbons from host to parasite during usurpation has been documented, hydrocarbon profiles of newly mated and established Formica queens were not readily distinguishable. This suggests that other compounds may signal the suitability of a host queen and colony. The results reported here may impact the successful implementation of parasitic ants in the biological control of fire ants.

Technical Abstract:
The evolutionary success of the slave-maker ant genus Polyergus stems from their specialised ability to exploit the foraging, feeding, and brood care behaviours of their Formica host species at all stages of the parasite life cycle. A new Polyergus colony is initiated when a newly mated gyne invades a host Formica species nest and kills the resident queen. This process results in chemical camouflage of the invading gyne and allows her to usur the position of colony reproductive. Polyergus gynes, however, do not attack young Formica gynes. To determine whether P. breviceps gynes target host queens on the basis of worker and/or brood presence, we placed eggs, larvae, pupae, and workers from mature Formica gnava queens with newly mated F. gnava queens and observed the ensuing responses of introduced P. breviceps queens. No newly mated gynes were attacked. We also tested newly mated F. gnava queens 1) once they had produced eggs, 2) when those offspring reached the larval, pupal, and callow stages of development, and 3) every two weeks until aggression ensued. Not until 29 weeks after F. gnava queens had mated did P. breviceps queens attack all the newly mated F. gnava queens tested. This suggests that, P. breviceps queens are able to detect mature queens using a time-dependent feature, one that might be a reliable indicator of reproductive status. In other ant species dominant queen status has been correlated with cuticular hydrocarbon profiles. Hydrocarbon profiles of newly mated and established F. gnava queens, however, were not distinguishable, suggesting that queens use other cues that signal queen and colony suitability. Nonetheless, our findings indicate that P. breviceps queens avoid attacking F. gnava queens that are unable to supply an immediate work force.

Interpretive Summary: Parasitic ants are ant species that have evolved mechanisms to integrate in their host ant species. The process involves some form of host queen usurpation by the parasitic ant queen(s). This generally leads to the premature death of the parasitized colony. Understanding this process is interesting evolutionarily and for reasons related to the potential use of parasitic ants in the biocontrol of pest ant species. Scientists at the Center for Medical, Agricultural, and Veterinary Entomology, USDA, ARS, Gainesville, Florida, The City University of New York, and Clarkson University, Potsdam, New York, determined that newly mated queens of the slave-maker parasitic ant species, Polyergus breviceps, are able to differentiate immature host Formica colonies from mature colonies. This ability increases the survival rate of the parasitic species, since they require fully mature host colonies to provide their slave work force. The cues are likely to be chemical in nature. While the transfer of cuticular hydrocarbons from host to parasite during usurpation has been documented, hydrocarbon profiles of newly mated and established Formica queens were not readily distinguishable. This suggests that other compounds may signal the suitability of a host queen and colony. The results reported here may impact the successful implementation of parasitic ants in the biological control of fire ants.

Technical Abstract:
The evolutionary success of the slave-maker ant genus Polyergus stems from their specialised ability to exploit the foraging, feeding, and brood care behaviours of their Formica host species at all stages of the parasite life cycle. A new Polyergus colony is initiated when a newly mated gyne invades a host Formica species nest and kills the resident queen. This process results in chemical camouflage of the invading gyne and allows her to usur the position of colony reproductive. Polyergus gynes, however, do not attack young Formica gynes. To determine whether P. breviceps gynes target host queens on the basis of worker and/or brood presence, we placed eggs, larvae, pupae, and workers from mature Formica gnava queens with newly mated F. gnava queens and observed the ensuing responses of introduced P. breviceps queens. No newly mated gynes were attacked. We also tested newly mated F. gnava queens 1) once they had produced eggs, 2) when those offspring reached the larval, pupal, and callow stages of development, and 3) every two weeks until aggression ensued. Not until 29 weeks after F. gnava queens had mated did P. breviceps queens attack all the newly mated F. gnava queens tested. This suggests that, P. breviceps queens are able to detect mature queens using a time-dependent feature, one that might be a reliable indicator of reproductive status. In other ant species dominant queen status has been correlated with cuticular hydrocarbon profiles. Hydrocarbon profiles of newly mated and established F. gnava queens, however, were not distinguishable, suggesting that queens use other cues that signal queen and colony suitability. Nonetheless, our findings indicate that P. breviceps queens avoid attacking F. gnava queens that are unable to supply an immediate work force.